Wild Side: Restore the St. Croix River by limiting what flows into it

• St. Croix River near Scandia

Backwater on the St. Croix River near Scandia, Minn., in June last year. Note the dense floating mat of filamentous algae. Randy Ferrin photo

Talk about it

In 1968 Congress passed the Wild and Scenic Rivers Act.

The St. Croix National Scenic Riverway, including its tributary the Nemekagon, was one of the original eight rivers included in the act. The lower 52 miles of the St. Croix River were added to the system in 1972.

The St. Croix River Valley began to become more densely populated and agricultural practices became more intensive in the mid-1900s. Municipal waste discharges, urban stormwater runoff, and non-point source runoff conveying manure, sediment and fertilizer from agricultural areas increased loading of phosphorus to tributaries and on to the St. Croix.

Phosphorus is the primary nutrient limiting the abundance of algae in fresh water. Increased phosphorus loading results in algae blooms. Mats of filamentous green algae and blue-green algae blooms are especially noxious, putting the “yuck” into prospects for swimming. When high-density algae blooms die, they release toxins and take up dissolved oxygen from the water degrading habitat for fish and other aquatic life.

The Federal Clean Water Act requires states to identify waters that are not meeting water quality standards and supporting designated uses. Water quality in the St. Croix River Basin, including Lake St. Croix, has been studied for more than 30 years. Both Wisconsin and Minnesota have determined that water quality in Lake St. Croix is impaired, not meeting water quality standards for nutrients due to excess phosphorus concentrations.

When impaired waters are listed the states are required to quantify the amount of pollutant that the water body can receive without exceeding water quality standards and to apportion the allowable load among sources of the pollutant. The maximum allowable rate of pollution is called the Total Maximum Daily Load (TMDL). Think of it like how much chocolate you can eat in a day without getting sick.

The Minnesota Pollution Control Agency and the Wisconsin DNR in partnership with the St. Croix Basin Water Resources Planning Team, the Science Museum of Minnesota and Barr Engineering Inc. prepared a TMDL report for Lake St. Croix and submitted the draft to the U.S. EPA in December last year.

In that report, the partners examined the historic changes in phosphorus loading to Lake St. Croix, the sources of phosphorus loading, set targets for future conditions, and allocated phosphorus loading reductions among the sources to meet the targets. The draft report is available on-line at: www.pca.state.mn.us/index.php/view-document.html?gid=15338.

It turns out that the Kinnickinnic and Willow River watersheds have the highest annual yield of phosphorus in the St. Croix Basin, each exporting more than 0.4 kg/ha (0.36 pounds per acre), reflecting the more urbanized and agricultural character of the watersheds.

During the 1990s, phosphorus loading to Lake St. Croix was 460 metric tons per year, corresponding to an average growing season concentration in the lake of 51 micrograms per liter. The targets set by the states for phosphorus in Lake St. Croix are to reduce loading to the 1940s rate of 360 metric tons per year and an average summer phosphorus concentration of 40 micrograms per liter. This would result in a shift back to a diatom-dominated algae community and increased water clarity. It’s great to see your feet when you are standing in the water up to your knees.

To restore Lake St. Croix water quality, communities and landowners in the St. Croix Basin will need to limit phosphorus discharges from wastewater treatment plants, reduce phosphorus in urban stormwater runoff and in runoff from agricultural land. This will require local support in communities and voluntary efforts by landowners to sustainably manage land and water resources.

Let’s do what we can to restore water quality on the St. Croix by not applying phosphorus to lawns, composting grass clippings and yard waste (don’t let it wash down the storm drains in town), by applying best management practices to reduce sediment, manure and phosphorus in runoff from farms, and by supporting efforts to upgrade municipal wastewater treatment plants to reduce phosphorus discharges.

We are fortunate to live near the beautiful St. Croix River. The St. Croix is a national treasure. Let’s work together to keep it that way.

Please send any comments and suggestions for this column to me at

wildside@rivertowns.net

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